package xin.nick.demo;

import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class TestD {
    public static void main(String[] args) {


        System.out.println((String)null);
//        System.out.println(String.valueOf(null));
        System.out.println(new String((byte[]) null));

        Map<String, ?> map = new HashMap<String, Object>() {
            private static final long serialVersionUID = 1L;
            {
                put("a", 1);
                put("b", 2);
                put("c", 3);
                put("d", 4);

            }
        };

        Set<String> set  = map.keySet();
        for(String key : set) {
            System.out.println(map.get(key));
//            map.remove(key);
        }


    }
    public void method3() {
        int a = 1;
        long b = 1;
        int c = a += b;
//            int d = a + b;
    }
}
